1. Field of the Invention
This invention relates to machine elements and mechanisms as used in control lever and linkage systems that are usually hand operated and that include a flexible transmitter. More specifically, the invention pertains to an overload safety fastener for yieldably mounting, within an aperture of a mounting plate, an end fitting that is attached to an outer flexible conduit of a motion transmitting control having an inner operating member reciprocable therein for transmitting motion.
2. Description of the Prior Art
Bowden transmission mechanisms are used for the remote control of parts. Such motion transmitting controls have an outer flexible conduit and an inner operating member reciprocable within the conduit for transmitting linear force or motion between two points. Such controls often follow a tortuous path. At bends in the conduit or where the inner operating member deflects within the conduit or where there is friction between the inner operating member and the conduit, loading is transferred from the inner operating member to the conduit. Loading of the inner operating member produces a load of equal magnitude but opposite sense (tension or compression) in the conduit. Loading to failure of the mechanism will usually result in the failure of the inner operating member. However, the conduit could also be damaged.
When designing push-pull control cables to transfer linear force and motion between two points, the cable sizes are often selected on the basis of the force that can be applied to the cable, rather than the force that needs to be applied to the cable for operation of the control. This results in using a larger cable than required to meet the system needs. Larger cables usually result in greater cost, larger bend radii, greater space requirements, more static friction, and more backlash than smaller cables.
By using adjustable stops on the input mechanism of the cable, the load applied to the cable can be limited to some extent. Stops alone are not sufficient in systems where the device on the output end has stops that must be reached, where the output device has a variable total travel, where high loads are applied through what is normally the output device, or where there are high inertia or viscous effects.
The use of a spring between a push-pull cable conduit end and a member fixed relative to the conduit end to yieldably provide overload protection for the conduit is shown in U.S. Pat. No. 2,321,780 that issued to Tondeur on June 15, 1943; U.S. Pat. No. 3,383,940 that issued to Brilando et al on May 21, 1968; and U.S. Pat. No. 3,407,684 that issued to Van Noord on Oct. 29, 1968. These patents do not suggest pre-loading the spring and isolating the preloaded spring stress from the conduit.
A pre-compressed coil spring provides an automatic take-up for lengthening and/or shortening a control conduit, as shown in U.S. Pat. No. 2,380,015 that issued to Batterson et al on July 10, 1945. A separate manually adjustable take-up is also provided within the control conduit.